1. Field of the Invention
This invention pertains to a vacuum interrupter and, more particularly, it pertains to a vacuum interrupter having an all ceramic enclosure.
2. Description of the Prior Art
Vacuum interrupters for electric circuits are comprised of an evacuated envelope in which a pair of separable electrical contacts are disposed for opening and closing a circuit. The envelope usually comprises a tubular housing and a pair of end plates. Generally, the tubular housing is comprised of a pair of cylindrical tubes made from an insulated material and end plates composed of metal. Examples of such vacuum interrupter are disclosed in U.S. Pat. Nos. 3,727,018; 3,818,163; 4,431,885; 4,438,307; 4,450,327; 4,540,863; and 4,630,361.
During opening of the contacts within the interrupter, an arc occurs between the contacts which is accompanied by a high temperature at the arc roots on the contact surface. As a result the contact metal vaporizes and produces metallic vapor and particles which disperse in all directions and deposit upon the interior surface of the envelope. Repeated opening operations of the contact would ultimately cause a metallic deposit on the insulating housing which would extend from one metal end plate to the other, thereby causing short circuiting conditions. For that reason, shields must be provided within the vacuum interrupter for preventing condensation and deposit of the metal particles on the interior insulating surfaces of the interrupter.
Associated with the foregoing is an additional precaution of replacing the metal end wall with insulating material, such as the ceramic material or glass, as disclosed in U.S. Pat. No. 3,944,771, whereby overcurrent protection is increased. Notwithstanding the advantages of a structure which eliminates metal end walls there is a need for a novel vacuum interrupter design and manufacturing technique therefor.